A researcher from a major London-based TV news show rang me on Friday to discuss the Ashers case.

We talked over the basics - the McArthur family, who own Ashers bakery, run a successful family business. Gareth Lee, a gay rights activist, asked Ashers bakery to make a cake with the slogan 'Support Gay Marriage' on it. Ashers were happy to sell Mr Lee a cake, but not to promote a view contrary to their firmly-held religious beliefs.

When they politely declined to bake the cake, they were taken to court in a case supported by the Equality Commission. They lost and are now appealing to the Supreme Court, which is sitting in Belfast this week for the first time ever.

But isn't that unfair to gay people, the London researcher asked me. I explained that Mr Lee had been served by Ashers before and they would happily serve him again. "Oh" she said, seeming a little surprised by this, but she persisted that it seemed unfair. I explained that if I, the chief commissioner or anybody, gay or straight, had asked them to make that cake they would have politely declined. "Oh" she said again sounding surprised.

She had one more attempt to point out the perceived unfairness to gay people. This time I explained that Peter Tatchell, the UK's leading gay rights campaigner, who had initially opposed Ashers, now supported their cause. He said: "Ashers did not discriminate against the customer, Gareth Lee, because he was gay. They objected to the message he wanted on the cake: 'Support gay marriage'."

There was one final "Oh" from the researcher. She hadn't realised Mr Lee had been served before, that the case was about the message not the customer, and that Peter Tatchell believed the case set a dangerous precedent. The researcher admitted she was a little behind in her knowledge of the case and that it now sounded much more interesting.

Northern Ireland's most famous cake was purchased almost four years ago and some are understandably tired by the whole saga. There is considerable ignorance about the facts of the case and the implications of the ruling. "Only in Northern Ireland," I heard someone comment. Except there is an almost identical case heading to the Supreme Court in America. The issue of free speech is a global one.

While the case has been portrayed as a battle between gay rights and religious freedom, it is actually about compelled speech and conscience. It has implications for everyone and that is why we should all care.

Discrimination against people is wrong. Ashers cannot and should not be able to discriminate against Mr Lee because he is gay. But discrimination against ideas is right and necessary in a free society - because some ideas are good and some are bad. The distinction is subtle but critically important.

This case is about forcing Ashers, or anyone for that matter, to use their skills to support a cause they disagree with. It tells people they can have their conscience or beliefs, but they are to be kept private. It is the State deciding which views it thinks are appropriate in the public square.

For the sake of a free and fair society, I for one hope and pray the Supreme Court will rule in favour of Ashers.

Peter Lynas is director of the Evangelical Alliance in Northern Ireland